December 15, 2008

Scientists Skeptical of Ocean-CO2 Capture Schemes

The icy seas between Australia and Antarctica could become a money generator by engineering nature to soak up carbon dioxide and then selling carbon credits worth millions of dollars.

But many scientists believe the concept of using nature to mop up mankind's excess CO2 to fight global warming is fraught with risk and uncertainty.

An Australian research body suggests more research is needed before commercial ventures are allowed to fertilize oceans on a large scale and over many years to capture CO2.

Tom Trull, one of the report's authors, said he doesn't think the scientific community has even sat down to determine whether this would be a low-risk endeavor.

"We never even designed measurement programs to look at ecological change and the risks," said Trull, Ocean Control of Carbon Dioxide program leader at the Antarctic Climate and Ecosystems Cooperative Research Center (ACE CRC) in Hobart.

But according to researchers, sprinkling the ocean surface with trace amounts of iron or releasing other nutrients over many thousands of square kilometers promotes blooms of tiny phytoplankton, which soak up carbon dioxide in the marine plants.

Once the phytoplankton die, they drift to the ocean depths, along with the carbon locked inside their cells where it is potentially stored for decades or centuries in sediments on the ocean floor.

Now this natural carbon sink has come to the attention of companies who hope to commercialize it to yield carbon credits to help industries offset their emissions.

However, scientists are unsure exactly how much carbon can be captured and stored in this way, for how long, or the risks to ocean ecosystems from such large-scale geo-engineering.

The thought is that such schemes could possibly change species composition in the oceans, increase acidity or cause oxygen depletion in some areas, even promote the release of another powerful greenhouse gas, nitrous oxide.

The ACE CRC's analysis on ocean fertilization science is that: "Ocean fertilization may cause changes in marine ecosystem structure and biodiversity, and may have other undesirable effects."

"While controlled iron fertilization experiments have shown an increase in phytoplankton growth, and a temporary increase in drawdown of atmospheric CO2, it is uncertain whether this would increase carbon transfer into the deep ocean over the longer-term," it says.

They also say negative impacts are expected to increase with the scale and duration of fertilization. There are doubts that any damaging effects could be detected in time.

John Cullen, professor of oceanography at Dalhousie University at Nova Scotia in Canada, said it is very important to recognize that if deleterious effects increase with scale and duration of fertilization, detection of these cumulative effects may not be possible until the damage is already done.

"It is extremely important to look at the ecological risks of this kind of activity," he said.

The Southern Ocean plays the greatest role of all the oceans in soaking up vast amounts of CO2 emitted by nature or through burning of fossil fuels and deforestation.

The Southern Ocean, however, is depleted of iron and experiments have shown even small amounts of the nutrient can trigger phytoplankton blooms that can last for up to two months.

"Iron fertilization is no silver bullet for climate change -- which underscores the severity of the problem we have, and the urgency for immediate emissions reductions worldwide," said Climos founder and CEO Dan Whaley.

He suggests that it is still premature to judge iron fertilization as dangerous.

"Phytoplankton are nature's way of sequestering CO2 to the deep ocean, where nearly 90 percent of earth's carbon lies. Further, most everything we put up in the air is going to the deep ocean eventually. The only question is how long it takes," he said.

But many nations are remaining cautious and member states of two treaties that govern dumping of wastes at sea passed a non-binding resolution in October calling for ocean fertilization operations to be allowed only for research.

Parties to the London Convention and related London Protocol, part of the International Maritime Organization, signed the resolution that said member states were urged to use "utmost caution" to evaluate research proposals to ensure protection of marine life.

Commercial ventures would need to operate over huge areas of ocean for many years, according to Trull, who participated in the first ocean fertilization experiment in 1999, one of a dozen since conducted globally.

Ocean fertilization just using iron would likely hit an absorption limit of about 1 billion tons of carbon (3.7 billion tons of CO2) annually, or about 15 percent of mankind's total carbon emissions, the ACE CRC report said.

The report added: "That really puts the risk in context. We're talking about altering ecosystems of planetary scale for a benefit that won't actually relieve us from dealing with all the other issues, such as conservation or alternative energy generation."

---

Image CAption: Phytoplankton bloom in the South Atlantic (February 15, 2006) seen from space. NASA